A magnetic disk drive includes a rotating magnetic disk with circular data tracks and magnetic read and write elements in which a write head is typically aligned with (or to) a read head on a slider. During a recording operation, the slider positions the read head and write head which are suspended over the magnetic disk on an air bearing surface (ABS). The write head has bottom and top pole layers that are connected at a back gap region. The bottom and top pole layers each have pole tips that are separated by a write gap layer and terminate at the ABS. In a merged read-write head configuration, the bottom pole also serves as the second shield layer in the read head. An electric current is passed through coils formed around the back gap region to magnetize the bottom and top pole layers.
Referring to FIG. 1, a portion of a conventional write head is shown that includes a bottom pole layer 1, a middle write gap layer 2, and a top pole layer 3 formed along an ABS plane. The bottom pole layer 1 has a pole tip 4 and the top pole layer 3 has a pole tip 5 at the ABS plane. Applying a current to nearby coils (not shown) produces a magnetic flux 6 that passes through the top pole layer 3 and is concentrated at the write gap side of the top pole tip 5. As the write element of the head is moved over a magnetic disk (not shown), the magnetic flux 6 passes from the top pole tip onto a data track and then to the bottom pole tip and is called the gap field. A small flank field 7 is also produced which is minimized to avoid overwriting adjacent data tracks. The rate of writing data to the data track is referred to as recording frequency. Recording density may be increased by decreasing the size of the track width which is defined by the width of the top pole tip in the write head.
A trend in the industry is to increase the recording density and recording frequency which requires a higher saturation magnetic flux density (BS) and higher resistivity (ρ) in the top pole layer than provided by conventional write heads. A low coercivity (HC) is also desirable. A high resistivity is needed to reduce eddy current loss at high frequencies while a higher BS value in a pole layer enables higher recording density and prevents saturation of the pole tips. Unfortunately, electroplated FeCo or FeCoNi films that are generally used in the industry as top and bottom pole layers in a write head have a high BS value but a relatively low resistivity of less than 20 μohms-cm which limits the high frequency application of the films in magnetic recording heads. On the other hand, when an alternative film that has a high resistivity is employed as the top pole layer, the film usually has an unacceptably low BS value. Thus, it is desirable to implement a novel magnetic layer that has a BS value of at least 1.9 Telsa (T) and a resistivity of greater than 70 μohms-cm in order to simultaneously achieve high recording frequencies of greater than about 600 MHz and recording densities higher than 10 Gbit/in2.
Although magnetic layers in read and write heads may be deposited by a sputtering method, an electrodeposition technique otherwise known as an electroplating process is usually preferred because the sputtering process produces a magnetic layer with a large magnetocrystalline anisotropy and higher internal stress. Electroplating is capable of generating a magnetic layer with a smaller crystal grain size and a smoother surface that leads to a high BS value and low coercive force (HC). In an electroplating process, an electric current is passed through an electroplating cell comprised of a cathode, anode, and an aqueous electrolyte solution of positive ions of the metals to be plated on a substrate (cathode). The anode may have the same composition as the metal being plated. The substrate typically has an uppermost seed layer on which a photoresist layer is patterned to provide openings over the seed layer that define the shape of the metal layer to be plated. Once the metal layer is deposited, the photoresist layer and underlying seed layer are removed. The magnetic layers which become a bottom pole and top pole layer in a write head may be formed in this manner.
U.S. Pat. No. 6,538,845, a high specific resistance layer is formed on a soft magnetic top pole layer in a write head to allow higher recording frequencies and higher recording densities. However, the high specific resistance layer requires a protective layer to prevent cracking which increases the complexity of the fabrication process and is likely to drive up production cost.
A laminated pole layer is provided in U.S. Pat. No. 6,233,116 and is comprised of alternating layers of FeXN such as FeRhN having a high magnetic moment and an amorphous alloy that is Co based with a high resistivity. Flux may travel along or across laminating layers which are deposited by a sputtering technique.
In U.S. Pat. No. 6,682,826 and related U.S. patent application 2004/0023074, a Fe alloy that may be FeCoV with a Fe content of at least 60 atomic % is used as a soft magnetic undercoat film in a recording medium. Similarly, in related U.S. Pat. No. 6,677,061, a FeCoVNiN alloy with at least 5 atomic % V is disclosed as a soft magnetic undercoat film and FeCoV as a magnetization stabilizing film in a recording medium. Although a high BS value is mentioned, the cited references do not teach a high BS in combination with a high resistivity for pole layer applications in a write head.
A main pole comprised of FeCoNi is plated on a NiV seed layer in U.S. patent application 2003/0189786. A non-magnetic seed layer is chosen to promote a low coercivity and the desired resistivity in the main pole of a perpendicular writer.